"The physics of space fighting" Topic

gizmodo.com/5426453

This is a pretty neat article. I don't know if it really breaks any new ground but it is a nice concentrated discussion of the issues.

thank you

feed this to the sfconsim-l monster, light touchpaper, stand back :)

He has a lot of good points. Most I knew of, but using shielded gyroscopes instead of maneuvering thrusters was never an argument I had encountered before.

He does neglect one key element that will influence ship design: where to put the fuel. Given our current understanding, even the most exotic power systems we can conceive of will require enormous reserves of fuel,* especially for interstellar travel… and that fuel has to be stored somewhere. So how does that affect ship design and appearance?

*Solar sails exempted.

Just clean out Nibbler's litter tray once a week…

There is one hole in his reasoning though. To make space fighters more efficient one only needs to modify thackian beam…

If that quantum reactionless drive thing from last week actually works, you may not need reaction mass after all.

link

Thats a perpetual motion machine !

No it's not. You have to put energy into rotating the quantum particles, probably in excess of the delta-V you get out of the system. What's "weird science" about it is that you can get momentum without expelling reaction mass. Delta-V with no rocket. The math (apparently) checks out, if our understanding of QM is right.

I wonder if anyone will be able to build such a machine, and if so, will it be able to compete with VASIMIR and other ion engines? (I'll be shocked if it can compete with chemical rockets.)

Did that guy just describe some of the ships from the Lensman books with the spherical ships?

Nope, if my understanding of what that news article is saying is correct, this is essentially a 'grav drive' from SF literature. It consumes (probably massive amounts of) energy but does not consume reaction mass, just consumes the mass in the nuclear reactor you need to provide power. I think this theory still follows all known laws of Physics (as we currently understand them). This drive is NOT reactionless, it's just getting a reaction without throwing onboard fuel mass… You're applying E=mc^2 as your reaction mass, I think.

The Lensman ships actually violate Newton's Laws, in addition to Relativity. The Bergenholm drive violates inertia (hence the name inertialess), there's no explanation for how the ships move other than reactionless, *and* the ships greatly exceed C with no mention of increased thrust costs to get there (to E.E. Smith's defense, those books were written before Relativity was announced).

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That original article completely ignored passive detection of spacecraft. You can't hide your thermal signature (the international space station is detectable from the orbit of Mars, and an operating nuclear reactor raises that detection range to roughly the orbit of Jupiter). For that matter, a nuclear rocket's plume would be visible on Earth during the day!

Parzival, gyro manouevre is a very old idea – mostly because it's a really good real-world system – and features in so many Golden Age stories that I couldn't list them all :) The Sir Arthur C Clarke story 'Hide And Seek' hsa the cruiser using its gyros and thrusters to fast rotations, for example, though . . .

Ummmm . . . Lion, the 'Skylark' stories were written in the 1920s before Relativity was well known; The Lensman stories are from the late 1930s to 1940s, and violate Relativity not at all. Relativistic effects apply only to objects with mass and inertia ( Which is why massless photons can move at lightspeed ), and several theories derived from Einsteins work do not link mass and inertia as a single property of matter; Indeed, the hypothesis of the Higgs Boson specifically states that matter without the Higgs or shielded form the effects of the Higgs would no longer be restricted by Relativistic 'laws'.

Smith wrote that the Inertialess Drive was mentioned in legitimate physics textbooks ( A reference can be found later – Busy at present) and is not totally forbidden by Einstein, so that is why he used it in trying to make the Lensman books as Hrad SF as possible given the time they where written, as opposed to the pure adventure of the 'Skylark' series. But then, with the article above, it seems that practically anything is forbidden by 'physical laws' . . . :)

Hey, it's been something like 20 years since I've read any of the EE Smith books, cut me some slack!

My edited point about passive detection still stands, though.

Gyros don't get used now for much in satellites, unless you need a very very precise way of aligning something (like the Hubble).

It turns out that for the mass of the gyro, the housing, and keeping said gyro from being damaged during launch, hydrazine thrusters will do it for a significantly smaller amount of mass.

Gyros are also a source of heat on the ship – when you pull energy out of the gyro to pivot, you're going to be warming up the gyro housing…and anything that even nicks that gyro is going to destroy the ship.

Not saying it can't work, but I looked long and hard at it when designing AV:T, and I couldn't figure out how to get gyros to 'make sense' when you can assume nuclear propulsion.

I'd really love to sit that guy down and play AV:T with him sometime. :)

The article is very good, and makes a point that I often consider. Interplanetary space is more of like a complex freeway system. Also, low orbits allow quick response times to orbital changes but lotsa fuel. High orbits are slow to get anywhere because gravity isn't a factor, it's also not on your side. "Jump point" games like Sins of a Solar Empire give you sort of an idea about jump points. It would be nice to see jump points being available on a "timing" basis.

As for rotating in space, gyroscopes are far too heavy and slow to be of any use. Only structures like the Hubble use them, to keep them orientated on a target. For the minutes or even seconds that a space fight will last, rather have extra RCS fuel if you need that extra bit of emergency thrust for evasion.

EDIT: Oh, I see AdAstra said the same thing.

EDIT 2: He hasn't mentioned the problem of fuel slosh. When ~50% of your fuel starts pummeling around in your ship, that's a chaotic acceleration environment that's going to play havoc with everything – tracking, sensors, the lot.

That show, "The Universe: Space Wars", had some really nice bits:

YouTube link
TMP link

Dan

Great article. Thank you for posting.

Gyros =- Maybe so, but you can run out of reaction mass for thrusters, so gyros make a good backup as long as you have power. And what about laser gyros?

Lion, no offense meant. You usually are accurate about these things :)

Fuel slosh:

First assumes a liquid phase fuel doesn't it? Solid or gaseous wouldn't necessarily slosh.

And even liquid fuel can be held in a bladder arrangement with some constant pressure plunger feed mechanism to maintain a contained non-slosh environment. (just my first take on the a system to control that problem)

The biggest real problem with space combat never seems to be addressed; debris and Kessler Syndrome. Until these can be addressed all other points are moot to me. Why fight if every time you do an trajectory or orbit is lost.

Good point about bladders.

For a very good number of reasons, fuel will be cryogenic and liquid. Liquid cryogens are the best for high efficiency thrust, which will be an issue. Also, they will be vital for cooling the hull, soaking up hits from lasers and keeping it nice and stealthy against passive IR.

Bladders and such are already used for non-cryogen fuels though, as balloons are inflated to squeeze fuel out in zero-gee (where a half-filled tank is just full of random droplets). Cryogens are a problem though, and fuel slosh has resulted in many launch failures. Current fuel tanks use baffles to minimise these. Probably some metallic piston affair lined with teflon or something would be useful to get fuel out of a cylindrical tank.